In the production of foamed synthetic resin materials, e.g. foamed polyurethane, it is a common practice to incorporate, as a foaming agent, a gas under pressure into one of the liquid components which are to be mixed to form the reactive system discharged into a mold.
As is pointed out in the aforementioned application which is incorporated entirely herein by reference, it is important for the quality of the foamed products which are produced to maintain the gas content of the gas-charged liquid component substantially constant. For this it has been necessary to sample the gas-charged liquid component in its tank, and to carry out a series of determinations which are onerous and higly imprecise if prior art techniques are utilized.